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Some English ConstructionsTransformational Framework

October 2, 2012

Lecture 7

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Some things are hard with Context-Free Grammars

• Assignment of structures to discontinuous constituents– A man wearing earings walked by– A man walked by wearing earings

• Agreement– 3rd person singular subjects get an “s” on the end of the verb

(even though there may be a gap between the head of the subject and the verb)

• Certain regularities seem to be at the word sequence level (e.g., verbs such as “call up”)

• ** Assignment of structure to related sentences that may look different. E.g.,– John hit the ball – The ball was hit by John– Who did John see – John saw Mary

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Chomsky – generalized rewrite rules

Now a derivation could not be captured in a phrase structure tree – that is just 1 step in a derivation

1. Generate a phrase structure tree down to level of lexical categories

2. Insert lexical items according to lexical rules (this step yields a DEEP STRUCTURE

3. Perform transformations on this tree structure using rules (some obligatory, some optional)

4. Use morphological rules to read off the actual words

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Why look at this?

• This DEEP STRUCTURE is generally the level that people thought one should run semantics on – all sentences with same deep structure have the same underlying meaning.

• The transformational framework is not really used in NLP – but I find it useful to explain some of the data that we see. You will see other grammatical formalisms try to “recapture” many of the things the transformational grammar explains.

Helping Verbs in EnglishHelping verbs – auxiliary verbs – have, be, and the models (e.g., can, could, might, may, will)

• John could sing.• John has sung.• John was singing.• John could have sung.• John has been singing.• John could have sung.

• *John sing could.

• * John have could sing.• *John was having sung.• *John has could sung.

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Some Rules:

Aux -> (m) (have) (be) S-> NP Aux VP

Yes-No Questions

• John could sing.• John has sung.• John was singing.• John could have sung.• John had been singing.• John could have sung.

• Could John sing?

• Has John sung?

• Was John singing?

• Could John have sung?

• Had John been singing?

• Could John have sung?

• *Have John could sing?

• *Been John had singing?

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Transformational rule:

Given a declarative sentence with helping verbs, form a Y/N Q by moving the first helping verb to the left of the subject

Could we do it with phrase structure rule?

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VP

NPbe

beNPhave

haveNPM

S

)(

English Verbal InflectionA verbal following a modal always assumes its uninflected form

John could

Amy could gone

Sue must working

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sang*

singing*

sing

had*

has*

have

was*

been*

be

English Verbal Inflection II

• The perfect helping verb have requires the verbal element following it to be in its past-participle form

John has

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singing*

sing*

sung

English Verbal Inflection III

• The progressive helping verb be requires the verbal element following it to be in its present-participle form

John is

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sing*

sung*

singing

English Verbal Inflection IV

• The verbal element immediately to the right of the subject is inflected for tense and, except for modals, also for number and person of the subject

– They like music. (pres)

– They liked music. (past)

– We are eating.

– We were eating.

– We have been singing.

– We had been singing.

– We could be singing.

– We can be singing.

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English Verbal Inflection

• Information about the inflection should be associated with the verb that introduces it (not with the verb it attaches to.

• Tense marker should always be first

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ing) (be en) (have (m) Tns Aux

Affix Hopping – put endings where they belong

13)(4,23,0,1

4321

obligatory

Y

V

be

have

m

-

ing

en

Tns

- X

Y/N Questions with tense

• Note: the moved constituent seems to carry the tense

– Would he go?– *Will he went?– Has he been working?– *Have he is working?

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Subject-Aux Inversion (2nd Preliminary Version)

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)(3,0,12

321

optional

X

be

have

m

Tns - NP

What happens when no modal/have/be?

• Fred past arrive at the party past Fred arrive at the party

Do Support:

An occurrence of Tns that has not been able to undergo affix hopping must have do inserted to the left of it (obligatory)

Do+past Fred arrive at the party Did Fred arrive at the party.

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OK - That wasn’t too hard…

• All of the above things can be understood with a transformational analysis – but it is reasonable to write context-free rules that capture what we see.

• Other kinds of constructions make that a bit more difficult… wh-questions and relative clauses. Let’s take a look…

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Wh-Questions

Wh-Questions are introduced with some wh-word

What could Mary be singing?

What did you find?

Who has eaten the cake?

What did you find the dog on?

Whose dog was the man bitten by?

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Wh-Questions - Observations1. Many show the same type of inverted word order of subject helping verb as we saw with y/n questions

What could Mary be singing?

What did you find?

*What you find?

Who has eaten the cake?

Who found a dog?

Whose dog was the man bitten by?

*Whose dog the man was bitten by?

Could Mary be singing something?

Did you find something?

Has someone eaten the cake?

???

Was the man bitten by the dog?

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Wh-Questions

2. The questioned constituent, even though it appears at the beginning of a question, is actually “understood” as fulfilling some function within the sentence

What could Mary be singing?

What did you find?

Who has eaten the cake?

What did you find the dog on?

Whose dog was the man bitten by?

Mary could be singing a song.

I found a dog.

Mary has eaten the cake.

I found the dog on the pillow.

The man was bitten by John’s dog.

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The Transformational Story

• The sentence started out as a regular question and then:1. Subject-aux inversion was applied to turn it into a y/n

question

2. One of the NP’s was moved up to the front of the sentence (this was a wh-np)

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Subject-Aux Inversion

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)(4,0,23,1

4321

optional

X

be

have

m

Tns - NP-Q

Question Movement

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y)(obligator 4 0, 2, 3,1

4--------3----21-

Z - y][det - X - Q NP-wh

Relative Clauses

Clauses that further specify an NP – usually introduced by a relative pronoun – who, whom, which, that

• The police recovered the car that Fred stole.• The hat John was wearing made Sheila laugh.• The man who took the money ran away.• The safe that the man took the money from was

broken.

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Relative ClausesLet’s look at the clauses themselves…• The police recovered the car that Fred stole.

– *Fred stole– Fred stole the car

• The hat John was wearing made Sheila laugh.– *John was wearing– John was wearing the hat

• The man who took the money ran away.– * took the money– The man took the money

• The safe that the man took the money from was broken.– *The man took the money from– The man took the money from the safe 25

Transformational Story

• Deep structure has the whole sentence there (modifying the NP) – relative clause formation has us delete it (and perhaps add the relative pronoun).

• Non-transformational story – when you hit a relative pronoun – you expect to parse a sentence with a hole in it – that hole needs to be filled with the NP that is being modified by the relative clause…

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